A superposition model for corrosion fatigue formulated for reactor pressure vessel (RPV) steel is described in this paper. The three components of crack growth rate are associated to pure fatigue, true corrosion fatigue, and stress corrosion.

The true corrosion fatigue behavior can be correlated with the material properties with regard to the resistance to generalized corrosion: the stress corrosion behavior can be correlated to the stress corrosion susceptibility of the material/environment couple.

While in pure fatigue and true corrosion fatigue the crack growth rate is depending on the applied ΔK (following Paris law), the stress corrosion component is time dependent. The onset of the stress corrosion component is associated with a critical ΔK (ΔKC), whose is depending on frequency.

The meaning of ΔKC is discussed and compared with the classical stress corrosion parameter KISCC.

The good prediction obtained for RPV steels suggests to extend this approach to other materials; an application to AISI 304 stainless steel is proposed.